French Oil Mill Machinery Report

7/30/2019 French Oil Mill Machinery Report

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Report on Vibratory Stress ReliefPrepared by Bruce B. Klauba

Product Group Manager

FRENCH OIL MILL MACHINERY COPicqua, Oh

FRENCH OIL MILL MACHINERY is a manufacturer of liquid-solid separation equipment used in,

among others the Food and Chemical Processing Industries. This Report describes the successful use

of the system on bi-metallic (stainless and mild steel) press frames which, because they are bi-metallic,could not be effectively treated with TSR.

Use of the VSR process after all welding had been completed enabled these workpieces to exhibitsuperb dimensional performance during final machining, assembly, transport and installation.

PH: 800.332.9770FX: 888.964.3866


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VSR TECHNOLOGY's Vibratory Stress Relief System was chosen by FRENCH OIL MILL

MACHINERY (FOM) to stress relieve two feed oil processing Press Frames. FOM had

previously authorized the use of this type of stress relief equipment on workpieces done byoutside contractors, but this was the first time the VSR System was used in-house.

The workpiece weldments were L-Shaped and each was 250" L and weighed 6,000 Lbs. While

the workpiece was primarily mild steel, the design did include a stainless steel liner andplumbing. Since the workpieces were bi-metallic, they were poor candidates for thermal stress

relief.

In the past, stress relief of these workpieces had been performed in either of two ways:

(1) After the mild steel components of the workpiece had been completely fabricatedand thermally stress relieved, the stainless components were added;

(2) The workpieces were made in halves. Both the low-carbon and the stainlessmaterials were welded separately on each half. Each half was then vibration treated

off-site by an outside firm. The two halves were then returned to FOMwhere they were welded together.

Both methods left a great deal of stress in the workpiece which interfered with final machining

because of the dimensional instability. Using Vibratory Stress Reliefafterthe workpiece wascomplete, however, resulted in a significant improvement in dimensional stability during

machining. The VSR System is now an integral part of FOM's Quality Assurance Program.

VSR SETUP

There are five key aspects to the correct setup of a workpiece for Vibratory Stress Relief:

1. Locating and placing the load cushions under the workpiece:

Load cushions are specifically located and placed beneath the workpiece to

isolate it from the floor and to minimize workpiece dampening (allowing

resonanceto occur), and eliminate the cross-transfer of noise with surroundingshop equipment.

2. Locating, orienting, and clamping the Vibrator:

Vibrator location and orientation are determined by how to most effectivelypromote the resonance frequenciesof the workpiece. Generally, the Vibrator'saxis of rotation should be parallel to the length of the workpiece, and the Vibrator

located in the central 1/3rd of the part. The ideal Vibrator location is decided

after response to vibration has been sampled.


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3. Locating, orienting, and clamping the Accelerometer:

Accelerometer location and orientation are selected to maximize resonance

frequencydetection. This acceleration sensor is best placed on a corner of the

workpiece, and oriented so as to be most sensitive to either vertical deflections,

or those that are horizontal but perpendicular to the workpiece's length.

4. Setting the Vibrator's eccentrics:

Vibrator unbalance should be initially set at a low level to sample the workpiece's

response to vibration. It is increased if the workpiece displays little resonance

activity. The unbalance is adjustable over a range of 5100% of the availableunbalance.

5. Calibrating the Control Console and Plotter:

The responsiveness of the workpiece to vibration, especially at resonance

frequency, is an unknown. Therefore, the sensitivity input gain of the Plotter(which depicts workpiece acceleration) has to be adjusted, since different

workpiece configurations have significantly different responses to vibration. The

adjustment is easy to make, and after the Plotter adjustment is made, the setup iscomplete.

In order to perform effective vibration treatment, the workpiece must have the ability to respond

to the most effective form of vibration resonance that will cause stress relieving. In order tostress relieve a workpiece, a great deal of load (force) within that workpiece is needed. This

Vibrator imposed load combines with the residual stress within the workpiece to cause plastic

flow at the granular level of the material being treated, ie, short-distance rearrangement of thematerial.

The most effective means of using vibration to produce maximum load within the workpiece is

to tune upon the resonances.

To enable resonanceto take place, the rubber isolation cushions must be placed far from the

corners of the workpiece. If the cushions are placed underneath the corners, they only serve asshock absorbers, which minimizes the effect of vibration. Since only three points are needed to

determine a plane, three cushions are usually all that are needed in a VSR System setup. In the

case of these workpieces, one cushion was placed at the center of the workpiece along the leftside major Axis on the outer-edge; the other two cushions were placed on the opposite side, also

on the outer-edge of the workpiece, 18" either side of center.


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The Vibrator was located on one of five "cross-bars" that spanned the trough and were equally

spaced along the length of the workpiece. The Vibrator was clamped in place using the specialClamps (provided) which include machined bolt points which mate with the hardened steel

inserts in the Vibrator's mounting feet.

Initially, the Vibrator's unbalance was set at the minimum 0.15 in-Lbs. (5% of the unit's 3.0 in.-Lbs adjustment), which was too low to resonate the workpiece. When the unbalance was

increased to 0.45 in-Lbs (15%), the workpiece reached the levels ofresonancewhich causedstress relief.

The Accelerometer was located on the corner of the workpiece (on the short leg of the "L"), and

was oriented so as to be most sensitive to vertical deflections.

The XY Plotter required some gain adjustment of its Y-input (the vertical), so that the generated

chart not only showed the workpiece's resonance peaks, but also allowed some room for peakgrowth.

At this point in the procedure, it was still not known whether the setup would be effective instress relieving these workpieces. It is only after a VSR Treatment has begun, and a change in

the resonance pattern, a classic response to treatment with the VSR Process, occurs that an

operator knows that a setup is effective. It's important to note that with thermal treatment thereis no feedback from the workpiece until machining, inspection, or assembly takes place, while

with VSR Treatment, monitoring and documentation of the workpiece's response is real-timegenerated. The VSR System not only allows operator intervention, but also answers the

questions of whether a particular workpiece needs stress relief, when to do the stress relief, and

whether the workpiece would benefit from more than one treatment. Again, such questions can

be raised but never answered when using the thermal treatment process.

VSR TREATMENT

VSR Treatment is accomplished by driving the workpiece hard enough to cause changes in the

resonance pattern. Specifically, the resonance peakseither grow to higher amplitudes, shift tolower frequencies, or a combination of both. These changes are consistent with a change in the

rigidity of the workpiece. A stress relieved Workpiece, whether relieved actively, via thermal or

vibration treatment, or passively, via transport or long term storage, is less stiff than its stressedcounterparts. Many machinists and fabricators are familiar with this fact because they've

observed the difference while performing cold straightening operations.


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During VSR Treatment the most effective Vibrator speed that relieves stress is centered at the

resonance frequency. As stress is relieved, the charted peak either moves up, which means thereis an increase in workpiece acceleration, or shifts to the left, which means there is a decrease in

the workpiece resonance frequency. As mentioned previously, it's common that both changes

occur.

After the first peak has been successfully treated, the second peak, and then the third peak can be

tuned upon, held, and tracked as it changes. If more than three peaks are present, these too canbe tuned upon, although rarely do fourth or additional peaks respond the treatment of the initial

peaks has done the job.

The resonance patternstarts out as being rather unstable. As the peaks are tracked and thechanges occur, the pattern of peaks becomes more and increasingly stable, eventually showing

no remaining change.

Similarly, the workpiece starts out as being, most likely, dimensionally unstable. As the

resonance patternbecomes more stable, so do the dimensional stability characteristics of theworkpiece, ie, workpiece stability results from resonance patternstability.

The peak hold time required to cause these changes to take place is rather short. In the case of

these workpieces, 10 to 12 minutes (per peak) for the first and second peaks was all that wasneeded. The dwell time on each peak doesn't vary much with the norm being 5 to 15 minutes.

Treatments including before and after scan periods (which are automatically performed by thesystem) range from as little as 40 minutes, to 2 hours for massive workpieces (>75 Tons). The

FOM workpieces took 75 minutes to stress relieve, using the VSR TECHNOLOGY System.

CONCLUSION

As evidenced by the clear change in the resonance patternsof these workpieces, they exhibited,

as expected, good dimensional performance during machining, assembly, transport, and

installation. Further, only the use of VSR Technology could assure good dimensional behavior,since attempts to thermal stress relieve bi-metallic workpieces regularly causes even greater

problems. If VSR TECHNOLOGY's Vibratory Stress Relief System had not been utilized, the

stresses would have complicated the machining process and assembly. Proper utilization of the

VSR TECHNOLOGY System involves recognizing appropriate applications, executing a correctsetup, and carrying out the procedures which enable the System to work.. As with many forms

of applied technology, proper setup makes the job easy, quick and effective.


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Bruce Klauba has a degree in Physics and a Level II Vibration Analysis Certification from the American Society of Non-Destructive

Testing (ASNDT). As a pioneer in the cause and effect of Vibratory Stress Relief, Mr. Klauba was named chief inventor (Klauba etal.) in U.S. Patent 4,381,673, which is both an equipment and process patent describing advances in the technology. He has authorednumerous articles and original research papers on the subject, which have been published in leading magazines and periodicals.Published papers include:

1. "Use and Understanding of Vibratory Stress Relief", Productive Applications of Mechanical Vibration, 1983, American Society of

Mechanical Engineers.2. "Vibratory Stress Relief: Methods used to Monitor and Document Effective Treatment, A Survey of Users, and Directions for

Further Research", 2005, Trends in Welding Research, ASM International.A co-author in both papers, Dr. C. Mel Adams, is a leading authority in metallurgy and co-founder of MIT's Welding ResearchDepartment. In addition, Mr. Klauba has extensive experience in designing, building, and troubleshooting Industrial and Commercial

Electrical Controls with a focus on extending the performance and reliability of Electric Motors and the systems they power.


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Workpiece set-up. ThreeLoad Cushions were usedto isolate the Workpiece,

one beneath the pipeflange, the other twospaced 3' apart, on theopposite side.

Another view of setup. TheVibrator location shown, was thethird one tried before theVibrator's ful l speed range couldbe achieved (motor protectioncircuitry in the Console preventedfull speed range at otherlocations). Pipe flange nearmidpoint was dividing line forweld seam which, previously,

jo ined the two halves after stressrelief.

The mounted MV2-3A-EC1Vibrator during dwell timeon a 4.2g peak (vibratorimage is blurred due tooscil lation). VSR Vibratorsare designed to survive

such usage. The Vibratormotor was barely warmduring use.


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VSR-752 System Electronics;the Plotter is on the left, andthe Console is on the right.

Close-up of the Plotter whileVibrator was tuned to the firstpeak. Some response hasalready taken place. Stress relief

occurs rapidly at the beginning ofthe cycle due to the high levels ofpotential energy in Workpiece,which the Treatment then reducesby converting it to kinetic energy.

Close-up of VSR-752 Console.Note the digital readout shows0.86g, which is the output of the

Accelerometer in realengineering units. Calculationswhich compare the input force(ie, the output force of theVibrator) into the Workpiece, tothe force experienced by theWorkpiece at resonance, indicatethat the combination ofWorkpiece resonance and theset-up procedure usedmultiply the Vibrator's output 20to 200 times. NB: Significantlyhigher multipliers often occur.


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FRENCHOILMILLMACHINERYC

OMPANY

09/26/1996

VSRT

reatmentChart

Workp

iece#1

VibratorUnbalanceat15%

Workpiece

Acceleration

1K

RPM

Red=After

VSR

Treatment

Black=B

efore

VSRTrea

tment

5K4

.2


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FRENCHOILMILLMACHINERYCOMPANY

09/26/1996

VSRTreatmentChart

Workpiece#2

VibratorUnbalanceat15%

Purple=Before

VSRTreatment

Red=After

VSR

Treatment

P

rogressDots{

1K

R

PM

5K


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French Oil Mill Machinery Report

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